This invention relates to seismic resistant equipment platforms. The seismic resistant aspect of the invention relates specifically to specially designed equipment platforms which maintain their structural integrity during seismic events and thus have improved seismic stability (i.e., greater stability during a seismic event). Equipment mounted on such equipment platforms is thereby better protected from damage during seismic events because these equipment platforms are able to withstand seismic events of a greater magnitude than previously known platforms. Specifically, these inventive equipment platforms are suitable for zone 0-4 seismic locations, having satisfied all relevant requirements of Bellecore Network Equipment Building Systems (NEBS) Requirements GR-63-CORE (NEBS PR-NWT-0063). Examples of equipment which may be protected by such equipment platforms include telecommunications equipment, computer equipment, rack mountable electronic equipment, pharmaceutical processing equipment, and any other form of electronic or laboratory equipment.
The term "seismic event" used herein refers to an earthquake or other earth vibration which produces seismic waves (e.g., P waves, S waves, Love waves, or Rayleigh waves) which directly or indirectly shake, vibrate, twist, displace, or similarly disturb earth surface structures (e.g., buildings, bridges, homes, etc.). The term "seismic resistant" used herein refers to the characteristic or property of being resistant to damage during a seismic event (e.g., being resistant to damage when shaken, vibrated, twisted, displaced, or similarly disturbed).
In telecommunications and computing facilities, raised floors are often used to support equipment while providing space between a subfloor (the floor on which the raised floor is mounted) and the raised floor for cabling and ancillary equipment (e.g., heating and cooling equipment). A large variety of raised floors are available and are well suited for use in stable environments which lack seismic activity. The majority of raised floors consist of a plurality of pedestals disposed in a rectangular array at regular spacings and interconnected by a plurality of parallel beams (e.g., box or roll formed stringers (hereinafter "stringers")). Each pedestal usually consists of a base, a column, and a pedestal head, with the base of each pedestal being bolted or glued to the subfloor on which the raised floor is to be constructed. The stringers are normally mounted between adjoining pedestal heads. A plurality of removable floor panels are then spanned between adjacent stringers. These floor panels may be attached to the pedestal heads or left free-floating on stringers. In this manner, an entire raised floor can be constructed. Viewed as a whole, such a floor is essentially a plurality of cantilever beams (i.e., the plurality of pedestals) interconnected by floor panels and/or stringers.
While these floors function well in areas free from seismic activity (e.g., stable environments), few have been designed to withstand the substantial forces present during a seismic event. Because each pedestal acts as a cantilever beam, the bending moment of each pedestal is largest at its base. Therefore, during a seismic event, the base of each pedestal is most likely to fail first, each pedestal either snapping off at its base (if constructed from a brittle material) or forming a plastic hinge at its base when the bending moment becomes equal to the fully plastic moment of the pedestal (if constructed from a ductile material). In either case, most raised floors will either collapse or experience some other form of catastrophic failure during a large seismic event, necessarily damaging any equipment mounted on these raised floors. (Such floors are therefore termed "non-seismic" floors.)
In addition to the above described non-seismic floors, a number of raised floors exist which provide some seismic stability but at a level insufficient to protect the heavy equipment typically found in telecommunications installations in zone 4 seismic locations (i.e., insufficient seismic stability to restore up to 2000 lbs. of force at any resonant frequency). Typically, seismic stability is introduced to a raised floor by providing supplemental bracing between the raised floor's pedestals and the subfloor to which the pedestals are mounted so as to selectively strengthen each pedestal's base, or by substantially increasing the diameter of each pedestal (thereby also strengthening each pedestal's base). While somewhat effective for protecting large footprint equipment during seismic events, both techniques significantly reduce the amount of room available for cabling and ancillary equipment underneath the raised floor and both are unable to support the load demands of much of the equipment used in the telecommunications industry (particularly small footprint, bay frame type equipment). (For convenience, hereinafter non-seismic floors and other raised floors which have insufficient seismic stability for heavy equipment applications are referred to collectively as "conventional" raised floors and the various components which comprise such conventional raised floors are referred to as "conventional" components (e.g., conventional pedestals, conventional floor panels, conventional pedestal heads, and the like).)
One method for constructing a seismic resistant raised floor which is suitable for use with telecommunications equipment is to decouple the raised floor from the subfloor on which it is mounted. Such a method is disclosed in U.S. Pat. No. 4,922,670 to Naka et al. (hereinafter "the '670 patent"). The '670 patent discloses a seismic resistant raised floor wherein the floor's pedestals, stringers, and floor panels are interconnected to form one rigid body which is decoupled from the subfloor by pivot points at the base of each pedestal. While this configuration successfully reduces the large bending moment that would otherwise be present at the base of each pedestal (i.e., the location where the bending moment of each pedestal would be the greatest if each pedestal were rigidly coupled to the subfloor), such a configuration lacks lateral support because of the pivot point decoupling. An entire seismic floor of this type would have to be constructed to gain lateral support from the walls of the room in which the floor is located. If a free standing platform were constructed in accordance with the teachings of the '670 patent, without attaching the platform to any walls, the platform would lack lateral support (as it can pivot at the base of each pedestal) and as such would not be seismic resistant. Because the entire floor disclosed in the '670 patent must be constructed in order to provide protection during a seismic event, a major drawback of the raised floor of the '670 patent is the cost of building an entire floor which is seismic resistant when such protection is only required in areas where equipment is located.
A need therefore exists for a seismic resistant raised platform which does not require an entire seismic resistant raised floor to be constructed.
It is therefore an object of this invention to provide a seismic resistant equipment platform which does not require supplemental lateral support.
It is a more particular object of this invention to provide a seismic resistant equipment platform which is not decoupled from the subfloor on which it is mounted.
It is a further object of this invention to provide a seismic resistant equipment platform which can be coupled to a conventional raised floor so as to provide selective seismic stability within the conventional raised floor.